This invention relates to near field RF communicators such as active RFID tags or transponders and, for example, to a near field RF communicator having a modified modulation circuit and to methods and apparatus for deriving a clock signal from a received RF signal in an active RFID tag during modulation.
Near field RF communicators are often produced in silicon where designs produced by multiple proprietors must co-exist. Accordingly a near field RF communicator may be required to operate using a data modulation signal received from more than one source and/or from sources which use different operating voltages. It is desirable to derive a clock signal from a received RF signal in a near field RF communicator for use in demodulation of the signal and in other internal functions of the near field RF communicator. The H-field strength available for coupling to a near field RF communicator is variable and may not be known in advance and to protect a near field RF communicator from overvoltage conditions caused RF H-field signals coupled to its antenna. Thus, there is a need to protect a near field communicator from over voltage conditions caused by RF H-field signals coupled to its antenna.